Unsecured Borrowings - Unsecured Long-Term Borrowings (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Fixed-rate obligations	$ 140,182	$ 129,031
Floating-rate obligations	73,754	78,045
Total	213,936	207,076
U.S. Dollar [Member]
Debt Instrument [Line Items]
Fixed-rate obligations	100,104	92,846
Floating-rate obligations	42,825	47,850
Total	142,929	140,696
Non-U.S. Dollar [Member]
Debt Instrument [Line Items]
Fixed-rate obligations	40,078	36,185
Floating-rate obligations	30,929	30,195
Total	$ 71,007	$ 66,380